The reformer reactor 1 in FIG. 1 comprises a housing 2 with an inner wall 4, an outer wall 6 and side walls 8a, 8b. Inner wall 4 and side walls 8a, 8b define a reaction chamber 10 in which hydrocarbon fuel 20 and oxidizing agent 14 are brought together and an auto-thermal reaction can take place.
Inner wall 4 and outer wall 6 define a space 12 between them. The space 12 in turn forms a passage for oxidizing agent 14 between an oxidizing agent supply port 16 and an oxidizing agent inlet 18.
Additionally, reformer reactor 1 includes a catalyst 28 for catalyzing the auto-thermal reaction in reaction chamber 10. The catalyst 28 accelerates the auto-thermal reaction, but it is also possible to use a reformer reactor according to the present invention without a catalyst. The catalyst 28 is preferably a metal grid or ceramic monolith, but it is possible to use any other suitable substrate for the design of catalyst 28.
The oxidizing agent inlet 18 is formed as a plurality of orifices, particularly as holes and/or minute slits, the size, shape and location of which vary depending on the used oxidizing agent 14, the used hydrocarbon fuel 20 and their temperature. The plurality of orifices can have uniform size and shape, but it is also possible that the orifices vary in size and shape among each other. Preferably, the size of the orifices and the distance between the orifices and the fuel inlet are designed so that an optimal turbulent mixture is achieved and so that the oxidizing agent/fuel mixture is substantially completely homogenous before coming in contact with the catalyst 28. The distance D between the mixing zone (location of the orifices 18) and the catalyst 28 is also constructed so that the oxidizing agent achieves a mixture stabilization without causing auto oxidation of the oxidizing agent/fuel mixture.
Further, reformer reactor 1 has a hydrocarbon fuel inlet 22 which is located in side wall 8a of housing 2. Preferably, the fuel inlet 22 is formed as a fuel injector which provides a fuel spray in reaction chamber 10. A reformer gas outlet 24 is provided in the opposite side wall 8b of housing 2. Reformer gas 26 is a hydrogen rich gas which can be used for operating of fuel cells and is the product of the auto-thermal reaction.
As shown in FIG. 1, the reformer reactor 1 further comprises a preheating means 30 for preheating the hydrocarbon fuel 20. In FIG. 1, the fuel preheating means is illustrated as separate device 30, but it is also possible to integrate fuel injector 22 and fuel preheating means 30 into a single device. If the fuel injector 22 is additionally in heat conductive contact with the side wall 8a, heat generated in the reaction chamber 10 can be transferred to the fuel injector 22, where it can be used to preheat the hydrocarbon fuel 20.
In the following the operation of the reformer reactor 1 is described by means of the exemplary conversion of diesel as hydrocarbon fuel into hydrogen with an air/steam-mixture as oxidizing agent. The reaction for the conversion is auto-thermal.
According to the invention air and steam are mixed before the air/steam-mixture 14 is injected by oxidizing agent supply port 16 into space 12 which serves as air/steam passage for transportation of the air/steam mixture 14 from oxidizing agent supply port 16 to oxidizing agent inlet 18 of the reformer reactor 1.
On the way to the plurality of inlet orifices 18 in the inner wall 4 of housing 2 the air/steam-mixture 14 is preheated by heat transfer from the inner wall into the air/steam mixture, whereby the heat transfer also cools the inner wall 4 of reaction chamber 10. By cooling the inner wall 4 of the reaction chamber 10 the risk of diesel fuel molecules in the reaction chamber 10 burning to soot when hitting the reaction chamber wall, is reduced. The inner wall 4 of the reaction chamber 10 is heated by the substantially homogenous oxidation taking place in the reaction chamber 10 when oxygen coming from the air/steam-mixture 14 reacts with “lighter” hydrocarbon molecules of the diesel fuel 20 having shorter chains (CxHy+O2→CO2+CO+H2O).
The air/steam-mixture 14 is forced through the orifices 18 into the reaction chamber 10 of the reactor forming a substantially homogenous air/steam fume in the reaction chamber 10, where it is mixed with diesel fuel 20 being sprayed into the air/steam fume by means of fuel injector 22.
For a successful mixing of the diesel fuel 20 and air/steam fume 14 a substantially perfect atomization or vaporization of the diesel fuel 20 into the air/steam fume 14 is required in order to substantially prevent condensation of the fuel 20 or air/steam fume 14. Since such an unwanted condensation likely occurs due to temperature differences between the preheated air/steam fume 14 and the normally cooler diesel fuel 20, according to the invention, also the diesel fuel 20 is preheated by preheating means 30. A substantially perfect fuel atomization or vaporization and subsequent air/steam mixture is achieved by preheating the diesel fuel 20 to a temperature close to, but below the lowest boiling point of the fuel, whereby also heat for a substantially perfect atomization or vaporization is provided. Preferably, also the air/steam fume 14 is preheated to a temperature in the same range or higher than the temperature of the diesel fuel 20, whereby an elevated temperature between fuel 20 and steam 14 is provided, which in turn substantially prevents condensation.
Since fuel, and particularly diesel fuel, is a mixture of different components, whereby each of which has a different boiling point, the air/steam mixture is preferably preheated to a temperature higher than the boiling point of the lightest components of the diesel fuel which defines the lowest boiling point of the diesel fuel. If the temperature of the preheated air/steam mixture is higher than the temperature given by the lowest boiling point of the diesel fuel, the light components of the fuel are substantially prevented from condensation and the temperature of the fuel/air/steam mixture converges to the boiling points of the heavier components of the fuel, whereby the substantially complete vaporization of the fuel can be easier achieved. It should be noted that a condensation of the air/steam mixture due to coming into contact with the “cooler” preheated fuel does not take place, since the air/steam mixtures is not cooled below its boiling point when it comes in contact with the preheated fuel.
The combination of fuel preheating and mixing the atomized fuel with the air/steam fume results in a substantially completely homogenous reactant mixture that allows for substantially complete conversion of the hydrocarbon fuel which in turn allows for an efficient production of fuel cell grade hydrogen.
Dependent on the location, size, and distance between the orifices and the fuel injector 22, inside reaction chamber 10 a turbulent mixture of the air/steam-fume with the diesel fuel spray is achieved, so that the mixture is substantially completely homogenous before it comes into contact with the catalyst 28.
This substantially homogeneous gas mixture is then introduced into catalyst 28 where the hydrocarbons of the diesel fuel 20 are undergoing the auto-thermal reaction process. In the auto-thermal reaction process taking place inside the catalyst hydrogen (H), CO and CO2 are produced as dominant process products. These products are processed in subsequent steps outside the reformer with the aim to separate H from all other process products.